The present disclosure relates to a touch input sensing device, and more particularly, to a sensing device that may reduce a circuit area and uniformly maintain touch input sensitivity.
A display device, such as a liquid crystal display (LCD), an organic light-emitting display (OLED), etc., a portable transmission device, other information processing devices, etc. perform functions by using various input devices. In recent, a touch screen device is being frequently used in a portable phone, a smart phone, a palm-size PC, an automated teller machine (ATM) device, etc. as such an input device.
In recent, it is a trend that the touch screen is disposed on the screen, a character is written or a picture is painted by the contact of a finger or touch pen (stylus) with a touch panel, and a desired command is executed by the clicking of an icon. The touch screen device may discern whether the finger, touch pen, etc. is in contact with the screen and information on the contact position.
Touch screens may be generally classified into a resistive type and a capacitive type according to a method of sensing a touch.
The resistive type touch screen has a structure in which glass or a transparent plastic plate is coated with a resistive material on which a polyester film is covered. The resistive type touch screen senses a touch point by the detection of a change in resistance that appears when a screen is touched. The resistive type touch screen has a drawback in that the touch is not sensed when pressure is weak.
On the contrary, the capacitive type touch screen forms electrodes on both or either of the surfaces of glass or transparent plastic, applies a voltage to between two electrodes, analyzes a change in capacitance between two electrodes appearing when a finger is in contact with the screen, and senses a touch point.
In order for the capacitive type touch screen to sense the touch point, a circuit is needed which measures a capacitance that is formed by one electrode or between two electrodes. Such a capacitance measurement circuit has been mostly used in order to measure the capacitances of various circuits or devices, and as various portable devices provide touch input interfaces recently, a range to which the capacitance measurement circuit capable of sensing the contact and approach of a user is applied is being expanded.
A typical capacitance measurement circuit may use two operational amplifiers (OA) for a single measurement channel in order to remove DC noise or low-frequency noise. However, since two OAs are used for the single measurement channel, there is a drawback in that the area of the circuit increases. Also, each OA may have a fabrication error. Due to such a fabrication error, a measurement value at the single measurement channel may appear differently from design intent. However, since such a fabrication error may vary according to a measurement channel, there is a drawback in that a measurement result at each measurement channel is non-uniform.